Thermal barrier coating for reduced sintering and increased impact resistance, and process of making same

ABSTRACT

A composition is disclosed that includes an at least partially stabilized zirconia matrix with a stabilizer and a pentavalent oxide dopant. A coated article is disclosed for use in a high temperature a gas turbine. The coated article can include an yttria-stabilized zirconia, and a pentavalent oxide dopant. The pentavalent oxide dopant can reduce sintering of the thermal barrier coating.

STATEMENT OF GOVERNMENT RIGHTS

This invention was made, at least in part, with a grant from theGovernment of the United States (Contract No. N00019-96-C-0176, from theDepartment of the Navy). The Government may have certain rights to theinvention.

TECHNICAL FIELD

Embodiments relate to a thermal barrier coating. More particularly,embodiments relate to an article with a thermal barrier coating which isused in the gas path environment of a gas turbine engine. In particular,an embodiment relates to a gas turbine system which includes a coatedturbine blade which acts as a thermal barrier coating.

TECHNICAL BACKGROUND

A thermal barrier coating (TBC) system may be used to protect thecomponents of a gas turbine engine that are subjected to the highestmaterial temperatures. The TBC system usually includes a bond coat thatis deposited upon a superalloy substrate, and a ceramic TBC that isdeposited upon the bond coat. The TBC acts as a thermal insulatoragainst the heat of the hot combustion gas. The bond coat bonds the TBCto the substrate and also inhibits oxidation and corrosion of thesubstrate.

One currently used TBC is yttria-stabilized zirconia (YSZ), which iszirconia (zirconium oxide) with from about 3 to about 12 percent byweight yttria (yttrium oxide) added to stabilize the zirconia againstphase changes that otherwise occur as the TBC is heated and cooledduring fabrication and service. The YSZ is deposited by a physical vapordeposition process such as electron beam physical vapor deposition(EBPVD). In this deposition process, the grains of the YSZ form ascolumnar structures that extend generally outwardly from andperpendicular to the substrate and the bond coat.

To be effective, the TBC system must have a low thermal conductivity andbe strongly adherent to the article to which it is bonded undercontemplated use conditions. To promote adhesion and to extend theservice life of a TBC system, an oxidation-resistant bond coat isusually employed. Bond coats are typically in the form of overlaycoatings such as MCrAlX, where M is a transition metal such as iron,cobalt, and/or nickel, and X is yttrium or another rare earth element.Bond coats are also diffusion coatings such as simple aluminide ofplatinum aluminide. A notable example of a diffusion aluminide bond coatcontains a platinum intermetallic, e.g. NiPtAl. When a diffusion bondcoat is applied, a zone of interdiffusion forms beneath a diffusion bondcoat. This zone is typically referred to as a diffusion zone.

During exposure of the ceramic TBC and subsequent exposures to hightemperatures such as during ordinary service use thereof, bond coats ofthe type described above oxidize to form a tightly adherent aluminascale that protects the underlying structure from catastrophicoxidation.

The columnar structure of the TBC system is of particular importance toadherence of the coating and to the coating maintaining a low thermalconductivity. Beside gaps between columns, there also exists a fineporosity within subgrains in the columnar structure. The fine porosityis sometimes observed to be oriented substantially orthogonal to thecolumns.

As the YSZ is cycled to elevated temperatures during service, sinteringcreates the problems of both the large-grain, inter-columnar porosityand the subgrain, fine porosity being gradually closed. As a result, theability of the YSZ to accommodate thermal expansion strains gradually isreduced, and the thermal conductivity of the YSZ gradually increases byabout 20 percent or more.

It has been recognized that the addition of sintering inhibitors to theYSZ reduces the tendency of the gaps between the columnar grains toclose by sintering during service of the thermal barrier coating. Anumber of sintering inhibitors have been proposed. However, thesesintering inhibitors have various shortcomings, and there is a need formore effective sintering inhibitors.

Some of the physical demands of a gas turbine blade include operation inextreme environments. One condition which a gas turbine blade issubjected to is the erosive effect of small particles which pass acrossthe turbine blade. The small particles can be generated a part of thecombustion process inside a gas turbine. Another condition which a gasturbine blade is subjected to is foreign objects which come into the gasstream.

What is needed is a TBC that avoids at least some of the problems thatexisted in the prior art.

SUMMARY

A component article of a gas turbine engine is disclosed. The componentarticle is applicable to a turbine blade or turbine vane. The componentarticle includes a body that serves as a substrate. Overlying andcontacting the substrate is a thermal barrier coating system such as abond coat. The bond coat includes an optional metal first layer that isa metal such as platinum or the like. The bond coat also includes ametal upper layer that is a metal such as aluminum or the like.

In one embodiment, the bond coat includes a diffusion zone that is theresult of interdiffusion of material from the bond coat with materialfrom the substrate. In one embodiment, the process that deposits themetal upper layer above the substrate is performed at elevatedtemperature, so that during deposition, the material of the metal upperlayer interdiffuses into and with the material of the substrate to formthe diffusion zone.

The structure of the turbine blade is completed with a ceramic thermalbarrier coating that overlies and contacts the bond coat surface and thealumina scale thereon. The ceramic thermal barrier coating includes anyttria-stabilized zirconia with at least one pentavalent oxide dopant ina concentration from about 1 mol percent to about 4 mol percent.

The bond coat includes the optional metal first layer, if present, themetal upper layer, and the alumina scale. In one embodiment, the bondcoat is a diffusion aluminide bond coat that is formed by depositing analuminum-containing metal upper layer over the substrate, and byinterdiffusing the aluminum-containing metal upper layer with thesubstrate. In one embodiment, the bond coat is a simple diffusionaluminde. In one embodiment, the bond coat is a more complex diffusionaluminide that includes another layer such as the metal first layer. Inone embodiment, the metal first layer is a platinum layer.

In one embodiment, the entire bond coat includes a platinum-aluminidediffusion aluminide. In this embodiment, a platinum-containing metalfirst layer is first deposited onto the surface of the substrate. In oneembodiment, other metals are used in place of or in addition to theplatinum to form the metal first layer.

After formation of the metal first layer, if present, the metal upperlayer is deposited above the substrate, and upon the metal first layerif present, by any operable approach. In one embodiment, an aluminascale forms at the bond coat surface by oxidation of the aluminum in thebond coat.

The ceramic thermal barrier coating is deposited by a process such asphysical vapor deposition process such as electron beam physical vapordeposition (EBPVD), or by the process of plasma spray deposition. In oneembodiment, the ceramic thermal barrier coating is a YSZ ceramic matrixwith at least one pentavalent oxide dopant added.

Examples include YSZ that has been modified with additions of a “third”oxide. In one embodiment, the “third” oxide includes a pentavalent oxideselected from vanadium oxide, tantalum oxide, niobium oxide,combinations thereof, and the like.

In one embodiment, the “third” oxide includes in addition to at leastone pentavalent oxide, a trivalent oxide selected from lanthanum oxide,combinations thereof, and the like. In one embodiment, the “third” oxideincludes one selected ytterbium oxide, gadolinium oxide, neodymiumoxide, combinations thereof, and the like. In each enumeratedembodiment, the “third” oxide is co-deposited with the YSZ.

When prepared by a PVD process, the thermal barrier coating is formedgenerally of a plurality of columnar grains of the ceramic material thatare affixed at their roots to the bond coat and the alumina scale. Insome locations of the thermal barrier coating, there are gaps that addto the insulative quality of the thermal barrier coating.

Processing is carried out by forming the optional bond coat over thesubstrate. Additionally, the optional platinum layer can be formedbefore forming the bond coat. To form the alumina scale, the bond coatcan be thermally treated. The thermal barrier coating is formed by adeposition process selected from electron beam physical vapor deposition(EBPVD) and plasma spraying.

These and other embodiments are set forth in the Detailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the manner in which embodiments are obtained, amore particular description of various embodiments briefly describedabove will be rendered by reference to the appended drawings.Understanding that these drawings depict only typical embodiments thatare not necessarily drawn to scale and are not therefore to beconsidered to be limiting of its scope, the embodiments will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 depicts a component article of a gas turbine engine such as aturbine blade or turbine vane;

FIG. 2 is a computer image cross section, through a portion of theturbine blade depicted in FIG. 1; and

FIG. 3 is a process flow diagram according to an embodiment.

DETAILED DESCRIPTION

The following description includes terms, such as first, second, etc.that are used for descriptive purposes only and are not to be construedas limiting. In the following detailed description, reference is made tothe accompanying drawings, which form a part hereof. These drawingsshow, by way of illustration, specific embodiments in which theinvention may be practiced. In the drawings, some of the like numeralsdescribe substantially similar components throughout the several views.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the invention. Other embodiments may beused and structural changes may be made without departing from the scopeof the several embodiments. Additionally, where compositions are given,if a composition is given with a percentage that is not modified by aterm such as mol %, volume %, etc. it is understood that the percentageis given in weight percent.

FIG. 1 depicts a component article of a gas turbine engine such as aturbine blade or turbine vane, and in this illustration a turbine blade100. The turbine blade 100 is formed of any operable material. Theturbine blade 100 includes an airfoil section 110 against which the flowof exhaust gas is directed. The turbine vane or nozzle has a similarappearance in respect to the pertinent airfoil section, but typicallyincludes other end structure to support the airfoil. The turbine blade100 is mounted to a turbine disk (not shown) by a dovetail 112 thatextends downwardly from the airfoil 110 and engages a slot on theturbine disk. A platform 114 extends longitudinally outwardly from thearea where the airfoil 110 is joined to the dovetail 112.

FIG. 2 is a computer image cross section, through a portion of theturbine blade 100. The turbine blade 100 is depicted in FIG. 2 as theairfoil section 110 of FIG. 1, and it is enumerated in FIG. 2 as item200. The turbine blade 200 has a body that serves as a substrate 216with a substrate surface 218. Overlying and contacting the substratesurface 218, and also extending downwardly into the substrate 216, is athermal barrier coating system 220 including a protective coating 222,which in this case is termed a bond coat 222. The bond coat 222 is thinand generally planar while conforming to and being bonded to the surface218 of the substrate 216. In one embodiment, the bond coat 222 is in athickness range from about 0.0005 inch to about 0.0 10 inch.

In one embodiment, the bond coat 222 includes an optional metal firstlayer 224 that is a metal such as platinum or the like. The bond coat222 also includes a metal upper layer 226 that is a metal such asaluminum or the like. In one embodiment, the bond coat 222 includes adiffusion zone 228 that is the result of interdiffusion of material fromthe bond coat 222 with material from the substrate 216. In oneembodiment, the process which deposits the metal upper layer 226 abovethe substrate surface 218 is performed at elevated temperature, so thatduring deposition, the material of the metal upper layer 226interdiffuses into and with the material of the substrate 216, to formthe diffusion zone 228. The diffusion zone 228, indicated by the dashedlines in FIG. 2, is a part of the thermal barrier coating system but itextends downward into the substrate 216.

In one embodiment, the bond coat 222 has an outwardly facing bond coatsurface 230 remote from the surface 218 of the substrate 216. In oneembodiment, a ceramic interface such as alumina (aluminum oxide, orAl₂0₃) scale 232 that forms at this bond coat surface 230 by oxidationof the aluminum in the bond coat 220.

The structure of the turbine blade 200 is completed with a ceramicthermal barrier coating 234 that overlies and contacts the bond coatsurface 230 and the alumina scale 232 thereon. The ceramic thermalbarrier coating 234 includes an yttria-stabilized zirconia with at leastone pentavalent oxide dopant in a concentration from about 1 mol percentto about 4 mol percent. In one embodiment, the pentavalent oxide dopantis in a concentration from about 1.3 mol percent to about 1.9 molpercent. In one embodiment, the pentavalent oxide dopant is in aconcentration from about 1.4 mol percent to about 1.8 mol percent. Inone embodiment, the pentavalent oxide dopant is in a concentration ofabout 1.6 mol percent.

Substrate Materials

Reference is again made to FIG. 1. In one embodiment, the componentarticle includes a component of a gas turbine engine such as a gasturbine blade 100 or vane (or “nozzle”, as the vane is sometimescalled). In one embodiment, the component article includes a singlecrystal substrate. In one embodiment, the component article is apreferentially oriented polycrystal, or a randomly oriented polycrystal.In one embodiment, the component article is made of a nickel-basesuperalloy for the substrate 216 (FIG. 2). As used herein, “nickel-base”means that the composition has more nickel present than any otherelement.

The nickel-base superalloys are typically of a composition that isstrengthened by the precipitation of gamma-prime phase or a relatedphase. In one embodiment, the nickel-base alloy has a composition, inweight percent, of from about 4 to about 20 percent cobalt, from about 1to about 10 percent chromium, from about 5 to about 7 percent aluminum,from 0 to about 2 percent molybdenum, from about 3 to about 8 percenttungsten, from about 4 to about 12 percent tantalum, from 0 to about 2percent titanium, from 0 to about 8 percent rhenium, from 0 to about 6percent ruthenium, from 0 to about 1 percent niobium, from 0 to about0.1 percent carbon, from 0 to about 0.01 percent boron, from 0 to about0.1 percent yttrium, from 0 to about 1.5 percent hafnium, balance nickeland incidental impurities.

In one embodiment, an alloy composition for the substrate 216 is Rene'N5, which has a nominal composition in weight percent of about 7.5percent cobalt, about 7 percent chromium, about 6.2 percent aluminum,about 6.5 percent tantalum, about 5 percent tungsten, about 1.5 percentmolybdenum, about 3 percent rhenium, about 0.05 percent carbon, about0.004 percent boron, about 0.15 percent hafnium, up to about 0.01percent yttrium, balance nickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 is Rene'N6, which has a nominal composition in weight percent of about 12.5percent cobalt, about 4.2 percent chromium, about 1.4 percentmolybdenum, about 5.75 percent tungsten, about 5.4 percent rhenium,about 7.2 percent tantalum, about 5.75 percent aluminum, about 0.15percent hafnium, about 0.05 percent carbon, about 0.004 percent boron,about 0.01 percent yttrium, balance nickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 is Rene'142, which has a nominal composition, in weight percent, of about 12percent cobalt, about 6.8 percent chromium, about 1.5 percentmolybdenum, about 4.9 percent tungsten, about 6.4 percent tantalum,about 6.2 percent aluminum, about 2.8 percent rhenium, about 1.5 percenthafnium, about 0.1 percent carbon, about 0.015 percent boron, balancenickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 is CMSX-4,which has a nominal composition in weight percent of about 9.60 percentcobalt, about 6.6 percent chromium, about 0.60 percent molybdenum, about6.4 percent tungsten, about 3.0 percent rhenium, about 6.5 percenttantalum, about 5.6 percent aluminum, about 1.0 percent titanium, about0.10 percent hafnium, balance nickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 isCMSX-10, which has a nominal composition in weight percent of about 7.00percent cobalt, about 2.65 percent chromium, about 0.60 percentmolybdenum, about 6.40 percent tungsten, about 5.50 percent rhenium,about 7.5 percent tantalum, about 5.80 percent aluminum, about 0.80percent titanium, about 0.06 percent hafnium, about 0.4 percent niobium,balance nickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 is PWA1480, which has a nominal composition in weight percent of about 5.00percent cobalt, about 10.0 percent chromium, about 4.00 percenttungsten, about 12.0 percent tantalum, about 5.00 percent aluminum,about 1.5 percent titanium, balance nickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 isPWA1484, which has a nominal composition in weight percent of about10.00 percent cobalt, about 5.00 percent chromium, about 2.00 percentmolybdenum, about 6.00 percent tungsten, about 3.00 percent rhenium,about 8.70 percent tantalum, about 5.60 percent aluminum, about 0.10percent hafnium, balance nickel and incidental impurities.

In one embodiment, an alloy composition for the substrate 216 is Mx-4,which has a nominal composition as set forth in U.S. Pat. No. 5,482,789,in weight percent, of from about 0.4 to about 6.5 percent ruthenium,from about 4.5 to about 5.75 percent rhenium, from about 5.8 to about10.7 percent tantalum, from about 4.25 to about 17.0 percent cobalt,from 0 to about 0.05 percent hafnium, from 0 to about 0.06 percentcarbon, from 0 to about 0.01 percent boron, from 0 to about 0.02 percentyttrium, from about 0.9 to about 2.0 percent molybdenum, from about 1.25to about 6.0 percent chromium, from 0 to about 1.0 percent niobium, fromabout 5.0 to about 6.6 percent aluminum, from 0 to about 1.0 percenttitanium, from about 3.0 to about 7.5 percent tungsten, and wherein thesum of molybdenum plus chromium plus niobium is from about 2.15 to about9.0 percent, and wherein the sum of aluminum plus titanium plus tungstenis from about 8.0 to about 15.1 percent, balance nickel and incidentalimpurities.

The use of the foregoing embodiments is not limited to these enumeratedalloys, and has broader applicability.

Bond Coat Materials

The bond coat 222 includes the optional metal first layer 224, ifpresent, the metal upper layer 226, and the alumina scale 232.

In one embodiment, the bond coat 222 is a diffusion aluminide bond coatwhich is formed by depositing an aluminum-containing metal upper layer226 over the substrate 216, and by interdiffusing thealuminum-containing metal upper layer 226 with the substrate 216. In oneembodiment, the bond coat 222 is a simple diffusion aluminde. In oneembodiment, the bond coat 222 is a more complex diffusion aluminide thatincludes another layer such as the metal first layer 224. In oneembodiment, the metal first layer 224 is a platinum layer.

Whether the bond coat 222 is a simple diffusion aluminide or a morecomplex diffusion aluminide, the aluminum-containing metal upper layer226 may be doped with other elements that modify the bond coat 222. Inone embodiment, the bond coat 222 includes an overlay coating known asan MCrAlX coating. The terminology “MCrAlX” is a shorthand term of artfor a variety of families of overlay bond coats that may be employed asenvironmental coatings or bond coats in thermal barrier coating systems.In this and other forms, M refers to nickel, cobalt, iron, andcombinations thereof. In some of these protective coatings, the chromiummay be omitted. The X denotes elements such as hafnium, zirconium,yttrium, tantalum, rhenium, ruthenium, palladium, platinum, silicon,titanium, boron, carbon, and combinations thereof. Specific compositionsare known in the art. Some examples of MCrAlX compositions include, forexample, NiAlCrZr and NiAlZr, but this listing of examples is not to betaken as limiting.

In one embodiment, the entire bond coat 222 includes aplatinum-aluminide diffusion aluminide. In this embodiment, aplatinum-containing metal first layer 224 is first deposited onto thesurface 218 of the substrate 216. In one embodiment, theplatinum-containing metal first layer 224 is deposited byelectrodeposition. In one embodiment, electrodeposition is accomplishedby placing a platinum-containing solution into a deposition tank anddepositing platinum from the solution onto the surface 218 of thesubstrate 216. An operable platinum-containing aqueous solution isPt(NH₃)₄HPO₄ having a concentration of about 4-20 grams per liter ofplatinum, and the voltage/current source is operated at about ½-10amperes per square foot of facing article surface. In one embodiment,the platinum metal first layer 224, is deposited in 1-4 hours at atemperature of 190-200° F. In one embodiment, the platinum metal firstlayer 224 is formed in a thickness range from about 0.00004 inch toabout 0.00024 inch. In one embodiment, the platinum metal first layer224 is about 0.0002 inch thick.

In one embodiment, other metals are used in place of or in addition tothe platinum to form the metal first layer 224. Such metals and theircombinations are known in the art.

After formation of the metal first layer 224, if present, the metalupper layer 226 is deposited above the substrate 216, and upon the metalfirst layer 224 if present, by any operable approach. In one embodiment,chemical vapor deposition (CVD) is used to form the metal upper layer226. In that approach, a hydrogen halide activator gas, such as hydrogenchloride, is contacted with aluminum metal or an aluminum alloy to formthe corresponding aluminum halide gas. Halides of any modifying elementsare formed by the same technique. The aluminum halide (or mixture ofaluminum halide and halide of the modifying element, if any) contactsthe platinum-containing metal first layer 224 that overlies thesubstrate 216, depositing the aluminum thereon. In one embodiment, thedeposition occurs at elevated temperature such as from about 1,825° F.to about 1,975° F. so that the deposited aluminum atoms interdiffuseinto the substrate 216 during a 4 to 20 hour cycle.

In one embodiment, an alumina (aluminum oxide, or Al₂0₃) scale 232 formsat this bond coat surface 230 by oxidation of the aluminum in the bondcoat 220 at the bond coat surface 230. Where the metal upper layer is acomplex aluminum compound, a modified “alumina” scale 232correspondingly forms the scale 232.

Thermal Barrier Coatings

The ceramic thermal barrier coating 234 is deposited by a process suchas physical vapor deposition process such as electron beam physicalvapor deposition (EBPVD), or by the process of plasma spray deposition.In one embodiment, the ceramic thermal barrier coating 234 has athickness from about 0.003 inch to about 0.010 inch thick. In oneembodiment, the ceramic thermal barrier coating 234 has a thickness ofabout 0.005 inch thick.

In one embodiment, the ceramic thermal barrier coating 234 is a YSZ,which is zirconium oxide containing from about 3 to about 12 weightpercent. In one embodiment, the ceramic thermal barrier coating 234 isfrom about 4 to about 8 weight percent, of yttrium oxide. Additionally,at least one pentavalent oxide dopant is added.

Examples include YSZ that has been modified with additions of a “third”oxide. In one embodiment, the “third” oxide includes a pentavalent oxideselected from tantalum oxide, niobium oxide, combinations thereof, andthe like.

In one embodiment, the “third” oxide includes in addition to at leastone pentavalent oxide, a trivalent oxide such as lanthanum oxide, andthe like. In one embodiment, the “third” oxide includes one selectedytterbium oxide, gadolinium oxide, neodymium oxide, combinationsthereof, and the like. In each enumerated embodiment, the “third” oxideis co-deposited with the pentavalent oxide and the YSZ.

In one embodiment, the ceramic thermal barrier coating 234 includes aceramic matrix of a doped zirconia with the addition of at least onepentavalent oxide. In one embodiment, the zirconia ceramic matrix is atleast partially stabilized with calcia and the addition of at least onepentavalent oxide. In one embodiment, the zirconia ceramic matrix is atleast partially stabilized with magnesia and the addition of at leastone pentavalent oxide. In one embodiment, the zirconia ceramic matrix isat least partially stabilized with ceria and the addition of at leastone pentavalent oxide. In one embodiment, the zirconia ceramic matrix isat least partially stabilized with a combination of at least two of theabove stabilizers and the addition of at least one pentavalent oxide.

In one embodiment, the zirconia ceramic matrix includes YSZ with about 4to about 8% by weight of yttria (which can be referred to as 4-8 YSZ).In this embodiment, the 4-8 YSZ matrix includes a pentavalent oxidedopant in a concentration from about 1 mol percent to about 4 molpercent. In one embodiment, the 4-8 YSZ matrix includes a pentavalentoxide dopant in a concentration of about 1.6 mol percent.

In one embodiment, the pentavalent oxide includes tantala, Ta₂O₅. In oneembodiment, the pentavalent oxide includes tantala in a major amount andat least one other pentavalent oxide such as niobia or niobium oxide. Inan alternative embodiment, the pentavalent oxide includes a tantalumoxide as a non-stoichiometric solid solution within the ceramic matrix.In another alternative embodiment, the pentavalent oxide includes atantalum oxide in a major amount as a non-stoichiometric solid solutionwithin the ceramic matrix, and at least one other pentavalent oxide suchas niobia or niobium oxide. In one embodiment, the pentavalent oxideincludes tantala in a range from about 1 mol % to about 4 mol %. In oneembodiment, the pentavalent oxide includes tantala in a range from about1.3 mol % to about 1.9 mol %. In one embodiment, the pentavalent oxideincludes tantala in a range from about 1.4 mol % to about 1.8 mol %. Inone embodiment, the pentavalent oxide includes about 1.6 mol % tantalain a 7 YSZ ceramic matrix.

In one embodiment, the pentavalent oxide includes niobia, Nb₂O₅. In oneembodiment, the pentavalent oxide includes niobia in a major amount andat least one other pentavalent oxide such as tantala or tantalum oxide.In an alternative embodiment, the pentavalent oxide includes a niobiumoxide as a non-stoichiometric solid solution within the ceramic matrix.In another alternative embodiment, the pentavalent oxide includes aniobium oxide in a major amount as a non-stoichiometric solid solutionwithin the ceramic matrix, and at least one other pentavalent oxide suchas tantala or tantalum oxide.

In one embodiment, the pentavalent oxide includes niobia in a range fromabout 1 mol % to about 4 mol %. In one embodiment, the pentavalent oxideincludes niobia in a range from about 1.2 mol % to about 1.8 mol %. Inone embodiment, the pentavalent oxide includes about 1.6 mol % niobia ina 7 YSZ ceramic matrix.

The thermal barrier coating 234 can include one of the various ceramicmatrix embodiments that are set forth herein. In one embodiment, yttriain the thermal barrier coating 234 is present in an amount of about 7%.The pentavalent oxide is selected from Ta₂O₅, tantalum oxide, Nb₂O₅,niobium oxide, and a combination thereof, and is present in a range fromabout 1 mol % to about 4 mol %. In one embodiment, the pentavalent oxideis selected from Ta₂O₅, tantalum oxide, Nb₂O₅, niobium oxide, and acombination thereof, and is present in a range from about 1.3 mol % toabout 3 mol %. In one embodiment, the pentavalent oxide is selected fromTa₂O₅, tantalum oxide, Nb₂O₅, niobium oxide, and a combination thereof,Ta₂O₅, tantalum oxide, Nb₂O₅, niobium oxide, and a combination thereof,and is present in a range from about 1.5 mol % to about 2 mol %. In oneembodiment, the pentavalent oxide is selected from Ta₂O₅, tantalumoxide, Nb₂O₅, niobium oxide, and a combination thereof, and is presentat about 1.6 mol %.

As illustrated schematically in FIG. 2, when prepared by a PVD process,the thermal barrier coating 234 is formed generally of a plurality ofcolumnar grains 236 of the ceramic material that are affixed at theirroots to the bond coat 222 and the alumina scale 232. The columnargrains 236 have grain surfaces 238. In some locations of the thermalbarrier coating 234, there are gaps 240, whose size is exaggerated inFIG. 2 for the purposes of illustration, between the grains 236 andtheir facing grain surfaces 238.

In one embodiment, the ceramic thermal barrier coating 234 is formed byEBPVD that forms a subgrain 242. The subgrain 242 is illustratedschematically in a selected portion of some of the columnar grains 236.In FIG. 2, the subgrain 242 includes a subgrain boundary and a subgrainbody. The subgrain boundary is depicted schematically as a diagonalline. The subgrain body is depicted schematically as the space betweentwo diagonal lines.

This morphology of the thermal barrier coating 236 including thecolumnar grains 236 with their corresponding gaps 240 and the subgrains242 is beneficial to the functioning of the thermal barrier coating 236.The gaps 240 allow the substrate 216, the bond coat 222 including thealumina scale 232, and the thermal barrier coating 234 to expand andcontract without significantly damaging morphological changes therein.Because the thermal barrier coating 234 is a ceramic material, it has agenerally low ductility so that the accumulated stresses would be likelyto cause failure. With the gaps 240 present, however, the in-planestresses in the thermal barrier coating 236 are developed across onlyone or at most a group of a few of the columnar grains 236. That is, allof the columnar grains 236 have in-plane stresses, but the magnitude ofthe in-plane stresses are relatively low because the strains do notaccumulate over long distances. The result is that the thermal barriercoating 234 with the columnar grains 236 and gaps 240 is less likely tofail by in-plane overstressing during service. Additionally, the gaps240 are filled with air, which when relatively stagnant between thegrains 236 is an effective thermal insulator, aiding the thermal barriercoating 234 in performing its primary role.

FIG. 3 is a block diagram of a process embodiment. The process 300includes forming the thermal barrier coating, and optionally forming thebond coating.

At 310, an optional bond coat is formed over the substrate.

At 312, the optional platinum layer is formed before forming the bondcoat.

At 314, the bond coat is optionally thermally treated to form the“alumina” scale 232 as set forth herein according to severalembodiments.

At 320, the thermal barrier coating is formed by a deposition processselected from EBPVD and plasma spraying.

EXAMPLE 1

An EB-PVD technique was used to form a coating on a substrate. Thecoating was 7 YSZ that included about 1.6 mol % of Ta₂O₅. After the TBCwas applied, thermal cycling (TC) was done to obtain a metric onsintering resistance. The coating was heated to about 1,200° C. forabout 2 hours in air. After the thermal cycling, the coated substratehad an observed change in thermal conductivity from about 1.58 W/m Kbefore TC to about 1.64 W/m K after TC, respectively. Evaluation of thethermal conductivity was conducted by the laser flash method known inthe art.

EXAMPLE 2

An EB-PVD technique is used to form a coating on a substrate. Thecoating is a 4-8 YSZ that includes a pentavalent oxide dopant in aconcentration from about 1 mol percent to about 4 mol percent. Afterforming the coating on the substrate, the coating on the substrate isexposed to about 1,200° C. for about 2 hours in air to obtain a metricon sintering resistance. After the heat treating of the coating, thermalconductivity of the coating has increased from about 2% to about 10%. Inone embodiment, thermal conductivity of the coating has increased morethan 10%, but less than about 20%.

EXAMPLE 3

An EB-PVD technique is used to form a coating on a substrate. Thecoating is a 7 YSZ that includes a pentavalent oxide dopant in aconcentration from about 1.2 mol percent to about 2.2 mol percent. Afterforming the coating on the substrate, the coating on the substrate isexposed to about 1,200° C. for about 2 hours in air to obtain a metricon sintering resistance. After the heat treating of the coating, thermalconductivity of the coating has increased from about 2% to about 9%.

COMPARATIVE EXAMPLE

An EB-PVD technique was used to form a coating on a substrate. Thecoating was a 7 YSZ. After the TBC was applied, TC was done by heatingthe coating to about 1,200° C. for about 2 hours in air. Seven baselinesamples were so processed, and an average of their tests was taken forthe baseline numbers. After the TC the coated substrate had an observedchange in thermal conductivity from about 1.53 W/m K to about 2.02 W/mK.

Gas Turbines

In one embodiment, a system is disclosed that includes a gas turbine. Inone embodiment, the gas turbine includes a composition and structuresimilar to the computer drawing depicted in FIG. 2. In one embodiment,the gas turbine includes a coated article according to embodiments setforth in this disclosure such as is depicted in FIG. 2. In oneembodiment, the gas turbine includes a turbine blade according toembodiments set forth in this disclosure such as is depicted in FIG. 1.

It is emphasized that the Abstract is provided to comply with 37 C.F.R.§ 1.72(b) requiring an Abstract that will allow the reader to quicklyascertain the nature and gist of the technical disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments of the inventionrequire more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive subject matter lies in lessthan all features of a single disclosed embodiment. Thus the followingclaims are hereby incorporated into the Detailed Description ofEmbodiments of the Invention, with each claim standing on its own as aseparate preferred embodiment.

It will be readily understood to those skilled in the art that variousother changes in the details, material, and arrangements of the partsand method stages which have been described and illustrated in order toexplain the nature of this invention may be made without departing fromthe principles and scope of the invention as expressed in the subjoinedclaims.

1. A composition comprising: a ceramic matrix including an at leastpartially stabilized zirconia and at least one pentavalent oxide dopantin a concentration from about 1 mol percent to about 4 mol percent. 2.The composition according to claim 1, wherein the at least at least onepentavalent oxide dopant is in a concentration from about 1.3 molpercent to about 1.89 mol percent.
 3. The composition according to claim1, wherein the at least at least one pentavalent oxide dopant is in aconcentration of about 1.6 mol percent.
 4. The composition according toclaim 1, wherein the at least partially stabilized zirconia isstabilized from at least one of yttria, calcia, magnesia, ceria, andcombinations thereof.
 5. The composition according to claim 1, whereinthe at least partially stabilized zirconia includes yttria in a rangefrom about 4% to about 8%.
 6. The composition according to claim 1,wherein the pentavalent oxide is selected from tantalum oxide, niobiumoxide, and combinations thereof.
 7. The composition according to claim1, further including at least one trivalent oxide selected from,lanthanum oxide, ytterbium oxide, gadolinium oxide, neodymium oxide, andcombinations thereof.
 8. The composition according to claim 1, whereinthe pentavalent dopant includes one selected from tantala (Ta₂O₅) andtantalum oxide as a non-stoichiometric solid solution, in a major amountand at least one other pentavalent oxide.
 9. The composition accordingto claim 1, wherein the pentavalent dopant includes one selected fromniobia (Nb₂O₅) and niobium oxide as a non-stoichiometric solid solution,in a major amount and at least one other pentavalent oxide.
 10. A coatedarticle, comprising: a superalloy substrate; a bond coat disposed abovethe superalloy substrate; a ceramic interface disposed above the bondcoat; and a thermal barrier coating disposed above the ceramic interfaceincluding an yttria-stabilized zirconia (YSZ) and a pentavalent oxidedopant in a concentration from about 1 mol percent to about 4 molpercent.
 11. The coated article according to claim 10, wherein theyttrium in the YSZ is about 7%.
 12. The coated article according toclaim 10, wherein the pentavalent oxide is selected from Ta₂O₅, tantalumoxide, Nb₂O₅, niobium oxide, and a combination thereof, and wherein thepentavalent oxide is present in a range from about 1.3 mol % to about1.9 mol %.
 13. The coated article according to claim 10, wherein thepentavalent oxide is selected from, tantalum oxide, niobium oxide, andcombinations thereof.
 14. The coated article according to claim 10,wherein the pentavalent oxide dopant includes one selected from tantala(Ta₂O₅) and tantalum oxide as a non-stoichiometric solid solution, in amajor amount and at least one other pentavalent oxide, and wherein thepentavalent oxide dopant is in a concentration range from about 1.2 molpercent to about 2 mol percent.
 15. The coated article according toclaim 10, wherein the pentavalent oxide dopant includes one selectedfrom niobia (Nb₂O₅) and niobium oxide as a non-stoichiometric solidsolution, in a major amount and at least one other pentavalent oxide,and wherein the pentavalent oxide dopant is in a concentration rangefrom about 1.2 mol percent to about 2 mol percent.
 16. A coated turbineblade comprising: a turbine blade substrate including a superalloy; aturbine blade coating above the turbine blade substrate, wherein thecoating is a composition including an yttria-stabilized zirconia (YSZ)matrix and a pentavalent oxide dopant in a concentration from about 1mol percent to about 4 mol percent.
 17. The coated turbine bladeaccording to claim 16, wherein the turbine blade coating includes a bondcoat including aluminum, and wherein the pentavalent oxide dopantincludes tantala in a range from about 1.3 mol % to about 1.9 mol %. 18.The coated turbine blade according to claim 16, wherein the turbineblade coating includes a bond coat including aluminum, and wherein thepentavalent oxide dopant includes niobia in a range from about 1.3 mol %to about 1.9 mol %.
 19. The coated turbine blade according to claim 16,wherein the turbine blade coating includes a bond coat includingaluminum, and wherein the pentavalent oxide dopant includes vanadia in arange from about 1.3 mol % to about 1.9 mol %.
 20. A system comprising:a gas turbine, and within the gas turbine a turbine blade, including: asuperalloy substrate; a bond coating disposed above the superalloysubstrate; a ceramic interface disposed above the bond coating; and athermal barrier coating disposed above the ceramic interface includingan yttria-stabilized zirconia (YSZ) and a pentavalent oxide dopant in aconcentration from about 1 mol percent to about 4 mol percent.
 21. Thesystem according to claim 20, wherein the pentavalent oxide dopantincludes from about 1 mol percent to about 2.2 mol percent tantala,niobia, or a combination thereof.